Building reliable interfaces between biological and engineered systems is one of the great challenges in biomimetic applications and for drug delivery purposes. A safe and effective adhesive can be very useful to implant a biomimetic microelectronic device inside the eye. Several adhesives such as hydrogels, fibrin sealants, and photocurable glues have been tested in previous studies for this purpose.1-3 These adhesives exhibit limitations such as inflammation, toxicity, insufficient adhesive strength, irreversibility and deformation of the ocular tissue.1-6 
Polymeric systems that may modify adhesive properties in response to changes in the physical and chemical characteristics of the physiological medium are promising candidates to achieve reversible tissue adhesion. Several groups have explored the use of dynamic stimulus-responsive surface chemistries for cell patterning.1,7-9 Thermo-active,7 electrical-active,8 and photo-active1,9 chemistries have been defined for cellular adhesion. In general, all of these chemistries operate under the same principle. These substances can be switched from a state that prevents cellular attachment to a state that promotes it.
A reversible, thermoresponsive adhesive could have many applications in opthalmology such as in posterior segment surgery, implantation of biometric microelectronic devices, and ocular drug delivery. Likewise, other sites in the body could benefit from a reversible bioadhesive strategy for localized delivery, surgical repair, or the attachment of prosthetic devices.
The ideal adhesive for intraocular use should be nontoxic and biocompatible. Previous reports showed that hydrogels such as SS-PEG and styryl-polyethylene glycol (ST-PEG) were effective but short-lasting and SS-PEG was toxic to the retina.1 N-isopropyl acrylamide (NIPAM) is toxic to neural tissue however, polymerized N-isopropyl acrylamide (pNIPAM) is not toxic to neural tissue and is commonly used in cell and tissue cultures for its reversible cell adhesion properties.11,15, 16 Previous reports showed that cells may be attached and detached from pNIPAM coated culture dishes without exhibiting any changes in morphology.11, 15 pNIPAM has also been used in retinal pigment epithelial (RPE) cell cultures to provide RPE sheets for transplantation. RPE cells also showed no signs of toxicity or changes in morphology.15 Interestingly, pNIPAM has also been used to stop bleeding in experimental liver injuries and no toxicity has been reported.17 In addition, previous studies show that pNIPAM has a lower critical solution temperature of 31° C. in an aqueous environment.11-12 This may indicate that the reversible thermoresponsive adhesive or hydrogel (pNIPAM) exhibits decreased solubility or swelling in water as the temperature is increased, due to a phase transformation at the lower critical solution temperature.11-12 Thus, pNIPAM may be switched from a state that promotes cellular attachment to a state that prevents cellular attachment, as the temperature of the surface is decreased.
More specifically, cell adhesion onto a pNIPAM substrate surface can be regarded as a two-step process, with the first step controlled by complex combinations of physiochemical interactions including hydrophobic, Coulombic, and van der Waals forces between the cell and the surface. This process is often called ‘passive’ according to this adsorption mechanism. The second step is considered ‘active’ because of the participation of cellular metabolic processes, including focal adhesion development as well as cytoskeletal reorganization. However, when the temperature is decreased below pNIPAM's lower critical solution temperature at 31° C. the polymer becomes readily hydrated and hydrophilic. Similarly, cellular activity-independent detachment is defined as ‘passive’ and cellular activity-dependent attachment as ‘active’.